Fluorescent lamps are common. A fluorescent lamp is substantially a gas discharge tube with a fluorescent material coated on an internal side thereof and argon filled therein. Neon or krypton may additionally be filled in the fluorescent lamp. The pressure in the fluorescent lamp is about 0.3% of that in the atmosphere. A small amount of mercury is filled in the fluorescent lamp to provide silver vapor. The amount of the silver atoms is about 1/1000 of that of all gas atoms. Electricity is directed through the fluorescent lamp to cause gas discharge. The gas discharge causes the mercury vapor to emit ultraviolet light with average wavelength of 2534 angstroms. About 60% of the electricity is converted to the ultraviolet light. The other electricity is converted to heat that is dissipated. The fluorescent material converts about 40% of the ultraviolet light to visible light. Therefore, the efficiency of the fluorescent lamp is about 24% (60%×40%), roughly twice as high as that of a typical tungsten light bulb.
As discussed above, the efficiency of a fluorescent lamp is low, and the life of a fluorescent lamp is short. As energy is running out while pollution is getting worse, it is important to increase the efficiencies and lives of devices as well as exploit so called “green” energy. There is a trend to use light-emitting diodes instead of the fluorescent lamps because the light-emitting diodes consume less energy, last longer, work more stably and efficiently than the fluorescent lamps.
However, a light-emitting diode generates a lot of heat while emitting light. A light-emitting diode will have to operate at a high temperature for a long time if it is used instead of a fluorescent lamp. The quality of the light-emitting diode will deteriorate so that the life will be reduced. Moreover, the efficiency of the light-emitting diode will drop so that the luminance will be reduced. Light-emitting diodes will be more popular if the problems associated with the heat are solved.
In a lamp, light-emitting diodes are provided in a tube with a rough internal side for scatter light emitted from the light-emitting diodes. The efficiency of this lamp is low.
In another lamp, light-emitting diodes and radiators are provided in a tube so that the radiators dissipate heat generated with the light-emitting diodes. The large amount of the light-emitting diodes however entails a high cost in manufacturing and a high cost in operation.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.